1. Field of the Invention
The present invention relates to an inter-shaft bearing for a multiple body turbo-engine fitted with means for controlling play during operation.
Some turbo-engines of the multiple body type comprise a bearing which rotatably supports a first shaft relative to a second shaft and which generally comprises bearing rollers disposed between an outer ring mounted on the first shaft and an inner ring mounted on the second shaft. This is particularly the case when the outer first shaft is constituted by the downstream journal of the shaft train of the high pressure body, and the inner second shaft is constituted by the downstream journal of the shaft train of the low pressure body.
2. Summary of the prior art
Apart from the intended mechanical functions of such bearings, arrangements are usually provided to ensure lubrication and cooling of the bearings, making use of various generally known solutions. An example of this is disclosed in European Patent Application No. 042 320, which also proposes the use of a film of pressurized oil to ensure the damping of vibrations of the shafts and the bearing which often arise during operation under the severe conditions occurring in high performance turbo-engines.
However, substantial play during operation may arise in some inter-shaft bearings, due, in particular, to differential expansions arising from thermal differences, and differences in centrifugal forces corresponding to different rotational speeds. European Patent Application No. 083 266 has proposed a partial solution by improving control over the temperature of a shaft by the circulation of oil in longitudinal channels provided inside the shaft. It has also been tried to fit a prestressed bearing or to use a collar, e.g. in accordance with U.S. Pat. No. 4,283,096.
The earlier mentioned European Patent Application No. 042 320 envisages mounting a shaft of the high pressure body, which is susceptible to being heated to higher temperatures and of rotating at higher speeds, inside the shaft of the low pressure body, which makes it possible to reduce play during operation. However, this type of assembly is not usable in certain applications and, in addition, it involves difficulties in determining the development of play during operation. Also, this solution, just as the solutions involving banding or prestressing, is subject to the risk of over-tightening during operation, which is prejudicial to the life of the bearing. Consequently, in the absence of a completely satisfactory solution, there remain in intershaft bearings, particularly in turbo-engines, problems of high amplitude vibrations and loads associated with the orbiting of the rotor of the high pressure body as a result of bearing play, which may become substantial during operation.